Sensor for the contactless detection of the level of a liquid and adhering high-conductivity medium, especially blood, through a non-metal wall of a container

摘要

The invention relates to a sensor for the contactless detection of the level of a liquid and adhering high-conductivity medium, especially blood, through a non-metal container wall. The sensor has a pulse generator (1) that generates brief pulses which, via a low-ohm resistor (2), namely, the measuring resistor, actuate an electrode (4) installed on the outside of the container wall. A fast-action difference amplifier that has a high common-mode rejection (6) and that taps a voltage drop at the measuring resistor (2) caused by the level-dependent pulse current, then said difference amplifier amplifies this voltage drop by a fixed factor and feeds the signal to a downstream peak detector (7) with filtering in order to obtain a level-dependent direct voltage and also feeds it to a downstream voltage comparator (8) which, by comparing the output voltage of the peak detector (7) to an adjustable setpoint voltage (9), generates a switching signal that changes from “low state” to “high state” as soon as a rising filling level causes the measuring electrode (4) to be sufficiently covered and conversely when the filling level sinks below the electrode (4) or reacts inversely to the change in the filling level as soon as the polarity of one of the stages consisting of the pulse generator (1), the difference amplifier (6), the peak detector (7) and the voltage comparator (8) is inverted.